1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having advantages of high contrast ratio, wide view angle and low color washout.
2. Description of the Prior Art
Since electrically controlled birefringence (ECB) LCD devices have advantages, such as higher aperture ratio and simple manufacturing process, the ECB LCD devices have become one of the widely prevailing LCDs nowadays. With reference to FIG. 1 and FIG. 2, FIG. 1 and FIG. 2 are schematic diagrams of a conventional ECB LCD panel. FIG. 1 is a schematic diagram illustrating a conventional ECB LCD panel in/under the bright state, and FIG. 2 is a schematic diagram illustrating a conventional ECB LCD panel in/under the dark state. The ECB LCD panel 10 is a normally white LCD panel. The ECB LCD panel includes two substrates 12, 14, and liquid crystal molecules 16 sealed therebetween. The liquid crystal molecules 16 are arranged along the rubbing direction on the surfaces of the substrates 12, 14. As illustrated in FIG. 1, when no voltage is applied between the two substrates 12, 14, the liquid crystal molecules 16 between two substrates 12, 14 are lying along the rubbing direction. In such a case, a polarized light, which enters the ECB LCD panel 10 from the back of the substrate 12 and penetrates through the liquid crystal molecules 16, can have a maximum phase difference. Consequently, the ECB LCD panel 10 displays the bright state. As illustrated in FIG. 2, when a dark state voltage (Vdark) is applied between the two substrates 12, 14, the liquid crystal molecules 16 is driven and rotated due to the electric field. In such a case, a polarized light, which enters the ECB LCD panel 10 from the back of the substrate 12 and penetrates through the liquid crystal molecules 16, can have a smaller phase difference. Consequently, the ECB LCD displays the dark state. However, the liquid crystal molecules 16 adjacent to the surfaces of the two substrates 12, 14 have a strong anchoring force due to the rubbing effect on the surfaces of two substrates 12, 14. Consequently, when a voltage is applied between the two substrates 12, 14, the liquid crystal molecules 16 adjacent to two substrates 12, 14 remain unaffected and are arranged along the originally rubbing direction. Under such condition, the liquid crystal molecules 16 adjacent to the surfaces of the substrates 12, 14 will influence the phase difference of the passing polarized light. As a result, when images are displayed in the dark state, viewers may see undesired light leakage from a wide angle. Furthermore, the contrast ratio of the LCD panel is also influenced.
In addition, the liquid crystal molecules 16 have dispersion characteristics. Therefore, the lights with different wavelengths have different phase differences when penetrating through the liquid crystal molecules 16. Consequently, the color washout problem occurs. For instance, since a blue light has a maximum phase difference when penetrating through the liquid crystal molecules 16. Therefore, when a black image is displayed, an excessively blue image often appears.